map projections used to transfer the image of the earth’s surface onto a flat surface no...

Map Projections

• used to transfer the image of the earth’s surface onto a flat surface

• no projection is an exact representation

• generally, the larger the area, the larger the distortion

• the 3 most common projections are cylinders, cones and planes

Cylindrical Projections

Mercator Projections • results when the contents of a globe are

transferred onto a cylinder of paper

Conic Projections• made by transferring the

contents of a globe onto a cone

• distortion increases north to south

• best used for land masses that have more area east to west (USA) than north to south (South America)

Planar Projections

Azimuthal Projections• made by transferring the

contents of a globe onto a plane

• the plane touches the globe at only 1 point, usually at the poles• very little distortion at that

point• distortion of direction,

distance and shape increase as the distance from the point of contact increases

West Wing Map Projection Clip

• http://www.youtube.com/watch?v=n8zBC2dvERM

Modern Map Making

Aerial Photographs

• taken from planes

• are very important to map makers in making accurate maps

• allow for a different perspective

Remote Sensing

• the gathering of information about a place without being there

• cameras in planes, satellites with sensors

• allow for very accurate maps

Information shown on maps

Title

• tells what area is being shown on the map or gives information about the map subject

– A Map of the Coast of East Florida from the River St. John Southward near to Cape Canaveral – 1791

– A Map of the New Governments of East and West FLORIDA. Inset of Pensacola – 1763

– A map of the peninsula of Florida showing the present field of surveying in the territory - 1846

– A Map of the Southern Indiana District of North America - - - Manuscript in Ayer Collection at the Newberry Library –1775

– A Map of the WEST INDIES... - 1715

Map’s scale

• shows the relationship between the distance on the earth’s surface and the distance on the map

Graphic scale “map’s ruler”

• the distance on the earth’s surface is represented by a bar graph that shows units of distance

Verbal scale

• is a phrase that describes a measure of distance on a map relative to the distance on the earth’s surface

UNITS VERBAL SCALE

inches 1 inch on the map = 62500 inches on the ground.

feet 1 foot on the map = 62500 feet on the ground

cm 1 cm on the map = 62500 cm on the ground

m 1 m on the map = 62500 m on the ground

Representative fraction • a fraction or ratio that shows the

relationship between the distance on the map and the distance on the earth’s surface

• it is unitless• it remains

constant no matter the measurement used

Compass rose

• shows how the map is positioned in relation to true north

Legend

• is a list of symbols used on the map and their explanations

Date

• gives the time at which the information on the map was accurate – County Map of Florida - 1872 – County Map of Florida - 1882

Topographic map • a map that shows surface features

(topography) of the Earth• natural features like rivers, lakes,

mountains• man made features

like cities, roads, bridges

• also show elevation

Elevation

• the height of an object above sea level

• sea level is 0

Topographic maps of the entire US were prepared by the Unites States

Geological Survey (USGS)

Contour lines • are lines that connect points of equal elevation

• are used to show elevation• the closer the contour

lines, the steeper the slope

• the more spread out the contour lines, the flatter the slope

• contour lines never intersect

contour interval • the difference in elevation between contour

lines• contour interval is chosen according to the

area’s relief

relief

• the difference in elevation between the highest point and the lowest point being mapped

index contour

• a darker, heavier contour line (usually every 5th line) that is labeled by elevation

• makes reading the map easier

hachures

• short, straight lines within a contour line

• indicate a depression

Reading a Topographic Map

Step 1 Contour lines never cross; all points along a

contour line are of the same elevation

Step 2 Closely spaced contour lines indicate a very

steep slope; widely spaced contour lines indicate a subtle slope

Step 3 Contour lines crossing valleys or streams

are “V” shaped. The “V” points to the higher elevation. If there is a river or stream in the valley, the “V” indicates the upstream direction.

Step 4Contour lines formed closed loops around hills,

mountains and depressions. Check for hachures.